Arrangement for dimming at least two parallel-arranged discharge lamps

ABSTRACT

An AC supply system for two or more parallel discharge lamps with means for dimming the lamps in steps. There are n ballast impedances for each lamp (n 2 or more) and n-1 diode bridges therefor. Each diode bridge is connected in series with at least one ballast impedance and in parallel with another ballast impedance. Two diagonal terminals of each diode bridge an connected to the corresponding diagonal terminals of the corresponding diode bridge for another one of the lamps. There are n-1 switching elements arranged to selectively interconnect the aforesaid diagonal terminals of the respective diode bridges in a manner such that the number of dimming steps is greater than the number of ballast impedances per lamp and wherein a failure of one or more lamps does not affect the light output of the remaining lamps.

United States Patent Jacques et al.

1451 July 25, 1972 ARRANGEMENT FOR DIMMING AT LEAST TWO PARALLEL-ARRANGED DISCHARGE LAMPS [72] Inventors: Jean-Marie Jacques, Bobigny; Maurice Beniada, Luneville, both of France [73] Assignee: U.S. Philips Corporation, New York, NY.

[22] Filed: June 24, 1970 [21] Appl. No.: 49,371

[56] References Cited UNITED STATES PATENTS Ulfiets ..3l5/201 FOREIGN PATENTS OR APPLICATIONS 1,169,035 4/1964 Germany ..3l5/DIG.4

Primary ExaminerNathan Kaufman Attorney-Frank R. Trifari 57 ABSTRACT An AC supply system for two or more parallel discharge lamps with means for dimming the lamps in steps. There are n ballast impedances for each lamp (n 2 or more) and n-l diode bridges therefor. Each diode bridge is connected in series with at least one ballast impedance and in parallel with another ballast impedance. Two diagonal terminals of each diode bridge an connected to the corresponding diagonal terminals of the corresponding diode bridge for another one of the lamps. There are n-l switching elements arranged to selectively interconnect the aforesaid diagonal terminals of the respective diode bridges in a manner such that the number of dimming steps is greater than the number of ballast impedances per lamp and wherein a failure of one or more lamps does not affect the light output of the remaining lamps.

10 Claims, 3 Drawing Figures PATENTEDJUL 2 5 I972 sum 1 OF 2 INVENTORS. JEAN-MARIE JACQUES MAURICE BENIADA AGENT PATENTEnJuL25 I972 3.679 .935 sum 2 or 2 Fig.3

I YE T OR J. JEAN-MARIE JACQUES MAURICE BENIADA BY AGENT ARRANGEMENT FOR DIMMING AT LEAST TWO PARALLEL-ARRANGED DISCHARGE LAMPS This invention relates to an arrangement for the alternatingcurrent supply of at least two parallel-arranged discharge lamps, which arrangement is provided with means for stepwise dimming of said lamps, each lamp having at least two ballast impedances.

In known arrangement of the above-mentioned kind (U.S. Pat. No. 3,178,610) the lamps are fed through a joint ballast inductance. A drawback thereof is that the current flowing through the joint inductance and hence the brightness of the lamps still operating vary when one of the lamps drops out. This results in a disturbing effect.

It is true that it is known to dim discharge lamps with the aid of an assembly of two anti-parallel thyristors connected in series therewith, but in that case it will often be necessary to take steps to reduce the influence of radio interference caused thereby, for example, by using special electric cables. In some cases it is, however, required to completely avoid radio interference and to have simple andlight-weight cables. This combination of requirements presents itself, for example, in the lighting installation of an airplane.

It is an object of the invention to provide a dimming arrangement without radio interference and using simple cables, wherein a lamp which drops out (becomes defective) does not cause a variation in brightness of the other lamps of the installation.

An arrangement according to the invention is characterized in that (n 1) bridge rectifiers are added to each lamp, in which n represents the number of ballast impedances for each lamp and in which two face-to-face diagonal points of each bridge rectifier are connected to the corresponding diagonal points of a bridge rectifier added to one of the other lamps, said two connections of corresponding diagonal points being connected together through a switching element. The path from the third to the fourth diagonal point of each bridge rectifier is arranged in series with one of the ballast impedances and is present in a branch shunted by one of the other ballast impedances.

A bridge rectifier (Graetz-bridge) is understood to mean an electric bridge having four branches each of which includes a diode and in which an electric (central) connection between two face-to-face angular points can be established, the diodes being polarized in such a manner that two bridge branches convey current in the case of a current-conveying central connection. A ballast impedance is understood to mean an inductance or a capacitance or a combination of both for stabilizing the lamp current.

An advantage of an arrangement according to the invention is that the brightness of the other lamps is not influenced when one of the lamps of the installation becomes defective, while furthermore switching thyristors are absent so there is no radio interference.

The ballast impedances of a lamp may be connected, for example, in parallel.

The ballast impedances added to a lamp are preferably connected in series.

An advantage of this preferred solution is that the relevant discharge lamp is extinguished when wire breakage occurs in a ballast impedance. This lamp might otherwise remain burning at a brightness deviating from that of the other lamps in the case of a parallel arrangement of ballast impedances. This gives a disturbing impression. This is certainly the case when, due to their ballast impedances being defective, a number of lamps would burn at brightness levels which are different from those of the other lamps of the installation.

In a further preferred embodiment of an arrangement according to the invention, wherein the number of ballast impedances for each lamp is at least three, the switching elements in the connection branches of the bridge rectifiers are free from mutual couplings so that the number of dimming positions is greater than the number of ballast impedances for each lamp.

An advantage of this preferred embodiment is that the number of dimming positions is comparatively great. The following will serve as an explanation. In the case of three ballast impedances for each lamp there are n-l 15-! 2 bridge rectifiers for each lamp. A total number of two switching elements is provided, namely one in each of the central connections of the two bridge rectifiers. Both switching elements may be either open or closed, or the first switching element may be open and the second may be closed, or the first may be closed and the second may be open. Thus there are four dimming positions, hence a greater number than the number of ballast impedances for each lamp, for this number was three.

A ballast for an arrangement according to the invention is preferably provided with a housing accommodating at least two ballast impedances, which housing also includes a bridge rectifier which is connected in series with one of the ballast impedances and which is present in a branch shunted by the other ballast impedance.

In order that the invention may be readily carried into effect it will now be described in detail by way of example with reference to the accompanying diagrammatic drawing, in which:

FIG. 1 shows an electric circuit of an arrangement according to the invention,

FIG. 2 shows a further electric circuit of an arrangement according to the invention, and

FIG. 3 diagrammatically shows a detail of a third arrangement according to the invention.

FIG. 1 shows a circuit of an arrangement according to the invention which is provided with two parallel-arranged lowpressure mercury vapor discharge lamps 13 and 13'. Three ballast impedances have been added to each lamp. These ballast impedances are connected in parallel. In FIG. 1 the reference numerals l and 2 denote terminals intended to be connected to an alternating voltage supply of, for example, 220 Volt, 50 Hz. The terminals 1 and 2 are connected through a two-pole switch 3 to a lead-through conductor 4 and a leadthrough conductor 5, respectively. The arrangement is provided with a few more lead-through conductors 6 to 9, which will be referred to hereinafter. A primary winding 10 of a transformer is connected to the conductors 4 and 5. A secondary winding 11 of said transformer feeds a preheated electrode 12 of the lamp 13. A further lamp electrode 14, which is likewise of the preheated type, is fed from a further secondary winding 15 of the transformer. The lead-through conductor 5 is connected through an inductance 16 to the preheated electrode 14 of lamp 13. In addition the conductor 5 is also connected to the electrode 14 through a bridge rectifier (Graetz bridge) 17 in series with an inductance 18. Finally the leadthrough conductor 5 is connected through a bridge rectifier 19 and a coil 20 in series therewith to the aforementioned electrode 14 of lamp 13. The said transformer (10, 11, 1S) and the coils 16, 18 and 20 and also the bridge rectifiers l7 and 19 are jointly incorporated in a ballast housing which is denoted by the reference symbol D D is shown by a broken line in FIG. 1.

FIG. 1 also shows a second lamp which is denoted by the reference numeral 13'. Similarly to the lamp 13, the lamp 13 is connected to the lead-through conductors 4 and 5. However, the reference numerals for the components in the circuit of the lamp 13' have indices. These components are present in the ballast housing D Finally a few connecting circuits are shown in the circuit of FIG. 1. There are two connecting circuits of the bridge rectifiers l7 and 17 and two connecting circuits of the bridge rectifiers l9 and 19. A first connecting circuit of the bridge rectifiers l9 and 19' is 19 connected to lead-through conductor 6. A second connecting circuit of the bridge rectifiers l9 and 19' is connected to the lead-through conductor 7. The lead-through conductors 6 and 7 may be connected together through a switch 21. A first connection of the bridge rectifiers conductors 8 and may be connected together through aswitch 22.

The operation of the circuit described is in broad outline as follows. When the switches 21 and 22 are set to theiropen position and-the switch 3 is closed, lamp 13 will receive current through ballast impedance 16 and lamp 13' will receive current through ballast impedance 16'. The electrodes of the lamps 13 and 13' are heated by the two transformers (10, ll, 15 and 10', 11', 15'). When the switch 21 is closed the bridge rectifiers l9 and 19 will also become active so that the lamps I3 and 13' are fed through the parallel-arranged inductances l6 and 20 and 16 and 20, respectively. As a result the brightness of the lamps l3 and 13 increases. When one of the lamps 13 or 13 drops out, no current can flow through the diodes from one lamp-circuit to the other lamp-circuit. When subsequently the switch 22 is closed each of the lamps is fed through three parallel arranged impedances. This leads to an increased brightness of the lamps. A further dimming position maybe obtained by opening the switch 21 when the switch 22 is closed.

FIG. 2 again shows the two discharge lamps 13 and 13 which likewise are low-pressure mercury vapor discharge lamps. This Figure also shows the two connecting terminals 1 and 2, the switch 3 and the lead-through conductors 4 to 9.

Also the two filament current transformers I0, l1, l5 and 10',

ll, 15' are shown in FIG. 2. The difference from the previous Figure is, however, that the ballast impedances are connected to the lead through conductor 5 in a different manner and that also the bridge rectifiers are connected in a slightly different manner. In particular the circuit of FIG. 2 is adapted in such a manner that the lead-through conductor 5 is connected to the preheated electrode 14 of the lamp 13 through a series-arrangement of three inductances 25, 26 and 27. Similarly the lead-through conductor 5 is connected to the preheated electrode 14' of the lamp 13' through a series arrangement of three inductances 25', 26' and 27 The inductance 25 is shunted by a bridge rectifier 28. The inductance 26 is likewise shunted by a bridge rectifier 29. Similarly the bridge rectifier 28 constitutes a shunt for the inductance 25'. Finally the bridge rectifier 29 constitutes a shunt for the inductance 26'. A first connection of the bridge rectifiers 29 and 29" is connected to the lead-through conductor 6. A second connection of the bridge rectifiers 29 and 29' is connectedto the leadthrough conductor 7. A first connecting line of the bridge rectifiers 28 and 28' is connected to the lead-through conductor 8 and a second connecting line of the bridge rectifiers 28 and 28' is connected to the lead-through conductor 9. The lead-through conductors 6 and 7 may be connected together by means of a switch 21. The lead-through conductors 8 and 9 may be connected together through a switch 22.

The circuit described differs from that of FIG. 1 by the fact that the inductances are now arranged in series, whereas they were arranged in parallel in FIG. I. In the closed state of the switches 21 and 22 the lamps of FIG. 2 burn most brightly, for in that case only the inductances 27 and 27 are the stabilizing impedances for the lamps l3 and 13. When the switches 21 and/or 22 are opened, more inductances are placed in the current circuits of the lamp so that the brightness decreases. The bridge rectifiers again prevent the brightness of a lamp from being influenced by the failure of the other lamp.

In FIG. 3, the reference numeral 50 diagrammatically shows the housing of a ballast. This ballast is connected to a lowpressure mercury vapor discharge lamp 51. The ballast 50 receives current through two supply wires which are connected' to the input terminals 52 and 53, respectively. Terminal 52 is connected to a terminal 54 and terminal 53 is connected to a terminal 55 of the ballast 50. In the circuit, which shows some conformity with that of FIG. 2, the lamp 51 is energized. In that case a filament current transformer 56 for heating the preheated electrode of the lamp 51 is used. Furthermore two inductances are provided which are denoted by the reference numerals 57 and 58, respectively. These two inductances are arranged in series. A bridge rectifier 59 shunts the inductance 58. The preheated electrodes are fed through secondary windings 60 and 61, respectively, of the said filament current transformer 56. An auxiliary capacitor 62 is incorporated between the primary winding of this transformer 56 and the secondary winding 61. The reference numerals 63 and 63a denote two output terminals of the ballast 50 which lead to one of the electrodes of the lamp 5!. The reference numetals 64 and 65 denote two further output terminals of this ballast 50 which are connected to a switch 66. Similarly as. for

7 example, the switch 21 of FIG. 2, the switch 66 serves to activate the bridge rectifier 59 so that the inductance 58 is shunted and the brightness of the lamp 51 is increased thereby. The assembly of components in the ballast 50 shown in FIG. 3 results in a very simple device. In an installation according to the invention a number of these devices cooperate. As has been described, a mutual influence of the lamps may be eliminated.

What is claimed is: V

1. An arrangement for supplying an alternating current to at least two parallel arranged discharge lamps with means for stepwise dimming of said lamps comprising, a pair of AC supply terminals coupled to said lamps, n ballast impedances connected in circuit with a first one of said lamps and another :1 ballast impedances connected in circuit with a second one of said lamps, wherein n comprises at least two ballast impedances for each lamp, a first group of (n-l) bridge rectifiers connected to said first lamp and a second group of (11-1) bridge rectifiers connected to said second lamp, means connecting two face-to-face diagonal points of each bridge rectifier of the first group to the corresponding diagonal points of a corresponding bridge rectifier of the second group to provide two such connections for each corresponding pair of bridge rectifiers. of the first and second groups, (n-l) switching elements, each of said two connected together through a respective switching element, and means connect- ,ing the third and the fourth diagonal points of each bridge rectifier in series with one of the ballast impedances and in a branch shunted by one of the other ballast impedances.

2. An arrangement as claimed in claim 1, wherein the ballast impedances for each lamp are connected in series.

3. An arrangement as claimed in claim 1 comprising at least three ballast impedances for each lamp and wherein the switching elements in the connection branches of the bridge rectifiers are free from mutual couplings so that the number of dimming steps for each lamp is greater than the number of ballast impedances for each lamp.

4. A ballast suitable for an arrangement as claimed in claim 1 and provided with a housing accommodating at least two of said ballast impedances, characterized in that the housing includes a bridge rectifier which is connected in series with one of said ballast impedances and which is present in a branch shunted by the other ballast impedance.

5. A lighting system for a plurality of discharge lamps comprising, first and second supply conductors adapted for con-' nection to a source of AC current, and means for coupling said lamps in parallel across said first and second supply conductors comprising, a group of n ballast impedances for each of said lamps wherein It comprises at least two ballast impedances per lamp, a plurality of diode bridges arranged in groups of (n'l) bridges for each lamp with each bridge arranged to pass an AC current through a first pair of diagonal bridge terminals, circuit means connecting said lamps to the supply conductors comprising means connecting said first pair of bridge terminals of each diode bridge in series with one of the ballast impedances and in shunt with another one of the ballast impedances of the associated group of impedances and diode bridges, means connecting a second pair of bridge diagonal terminals of each diode bridge of one group of bridges to the corresponding second pair of bridge diagonal terminals of corresponding ones of the diode bridges of a.

second pair of bridge terminals of a respective diode bridge in a manner to selectively interconnect said terminals of the respective diode bridges to adjust the current in steps in said lamps and thereby vary the lamp illumination.

6. A system as claimed in claim 5 wherein said circuit means comprises means connecting the ballast impedances of each group in series between one supply conductor and one terminal of its respective lamp and means connecting said first pair of bridge terminals of each diode bridge of its group to the terminals of its respective shunt impedance.

7. A system as claimed in claim 5 wherein said circuit means comprises means connecting a first ballast impedance of each group between one supply conductor and one terminal of its respective lamp, and means connecting each series combination of a ballast impedance and a first pair of terminals of a diode bridge of each group in parallel with the said first ballast impedance of its associated group.

8. A system as claimed in claim 6 which comprises at least three ballast impedances for each lamp and at least two switching elements which can be selectively operated to provide a greater number of current steps for each lamp than the number of lamp ballast impedances with a minimum of four such current steps in the case of three ballast impedances per lamp.

9. A system as claimed in claim 7 which comprises at least three ballast impedances for each lamp and at least two switching elements which can be selectively operated to provide a greater number of current steps for each lamp than the number of lamp ballast impedances with a minimum of four such current steps in the case of three ballast impedances per lamp,

10. A system as claimed in claim 5 wherein said circuit means comprises means connecting first and second ballast impedances of each group in series between one supply conductor and one terminal of its respective lamp and means directly connecting said first pair of terminals of a diode bridge of each group to the terminals of one of the impedances of its respective group. 

1. An arrangement for supplying an alternating current to at least two parallel arranged discharge lamps with means for stepwise dimming of said lamps comprising, a pair of AC supply terminals coupled to said lamps, n ballast impedances connected in circuit with a first one of said lamps and another n ballast impedances connected in circuit with a second one of said lamps, wherein n comprises at least two ballast impedances for each lamp, a first group of (n-1) bridge rectifiers connected to said first lamp and a second group of (n-1) bridge rectifiers connected to said second lamp, means connecting two face-to-face diagonal points of each bridge rectifier of the first group to the coRresponding diagonal points of a corresponding bridge rectifier of the second group to provide two such connections for each corresponding pair of bridge rectifiers of the first and second groups, (n-1) switching elements, each of said two connected together through a respective switching element, and means connecting the third and the fourth diagonal points of each bridge rectifier in series with one of the ballast impedances and in a branch shunted by one of the other ballast impedances.
 2. An arrangement as claimed in claim 1, wherein the ballast impedances for each lamp are connected in series.
 3. An arrangement as claimed in claim 1 comprising at least three ballast impedances for each lamp and wherein the switching elements in the connection branches of the bridge rectifiers are free from mutual couplings so that the number of dimming steps for each lamp is greater than the number of ballast impedances for each lamp.
 4. A ballast suitable for an arrangement as claimed in claim 1 and provided with a housing accommodating at least two of said ballast impedances, characterized in that the housing includes a bridge rectifier which is connected in series with one of said ballast impedances and which is present in a branch shunted by the other ballast impedance.
 5. A lighting system for a plurality of discharge lamps comprising, first and second supply conductors adapted for connection to a source of AC current, and means for coupling said lamps in parallel across said first and second supply conductors comprising, a group of n ballast impedances for each of said lamps wherein n comprises at least two ballast impedances per lamp, a plurality of diode bridges arranged in groups of (n-1) bridges for each lamp with each bridge arranged to pass an AC current through a first pair of diagonal bridge terminals, circuit means connecting said lamps to the supply conductors comprising means connecting said first pair of bridge terminals of each diode bridge in series with one of the ballast impedances and in shunt with another one of the ballast impedances of the associated group of impedances and diode bridges, means connecting a second pair of bridge diagonal terminals of each diode bridge of one group of bridges to the corresponding second pair of bridge diagonal terminals of corresponding ones of the diode bridges of a second bridge group, (n-1) switching elements, and means individually connecting each of said switching elements to the second pair of bridge terminals of a respective diode bridge in a manner to selectively interconnect said terminals of the respective diode bridges to adjust the current in steps in said lamps and thereby vary the lamp illumination.
 6. A system as claimed in claim 5 wherein said circuit means comprises means connecting the ballast impedances of each group in series between one supply conductor and one terminal of its respective lamp and means connecting said first pair of bridge terminals of each diode bridge of its group to the terminals of its respective shunt impedance.
 7. A system as claimed in claim 5 wherein said circuit means comprises means connecting a first ballast impedance of each group between one supply conductor and one terminal of its respective lamp, and means connecting each series combination of a ballast impedance and a first pair of terminals of a diode bridge of each group in parallel with the said first ballast impedance of its associated group.
 8. A system as claimed in claim 6 which comprises at least three ballast impedances for each lamp and at least two switching elements which can be selectively operated to provide a greater number of current steps for each lamp than the number of lamp ballast impedances with a minimum of four such current steps in the case of three ballast impedances per lamp.
 9. A system as claimed in claim 7 which comprises at least three ballast impedances for each lamp and at least two switching elements which can be selectively operated to provide a greater number of current steps for each lamp than the number of lamp ballast impedances with a minimum of four such current steps in the case of three ballast impedances per lamp.
 10. A system as claimed in claim 5 wherein said circuit means comprises means connecting first and second ballast impedances of each group in series between one supply conductor and one terminal of its respective lamp and means directly connecting said first pair of terminals of a diode bridge of each group to the terminals of one of the impedances of its respective group. 